Numerous watches display the day of the month in addition to the hour and minutes. Several solutions exist for achieving this:
The simplest solution consists in using a date ring on the periphery of which the numbers 1 to 31 are noted. The periphery of the date ring passes underneath an aperture arranged in the watch dial and reveals the day of the month. The date indications are regularly angularly distributed around the circumference of the ring.
It is clear that the size of the date indications depends upon the diameter of the ring. It is therefore understood that the larger the size of the date indications, the larger the radius of the date ring will be, and the more space the ring will require in the watch case.
To facilitate the reading of the date, it is evident that one solution is to increase the size of the date indications but with the aforecited limitation.
There are other possibilities for improving the readability of the date.
A first possibility consists of integrating a magnifying glass in the aperture in the dial through which the date indications appear.
Another solution consists in using two superposed date rings. One of these rings carries the numbers 1 to 15 and the other ring carries the numbers 16 to 31. An aperture arranged in the upper ring which moves above the other makes it possible to see the numbers on the lower ring. Spreading the date indications over two rings means that these indications can be larger.
Another principle consists of using two discs. One of the discs carries the tens numbers 0, 1, 2, and 3 while the other disc carries the numbers 0 to 9, namely the units. The two discs are arranged side-by-side, so as to form together the days of the month.
It is understood that the use of two date rings or discs complicates the mechanism, which rather restricts this type of solution to high end watches. Further, these solutions often have the effect of slowing down the change of date. In the case of the mechanism having two juxtaposed discs briefly described above, to change from the 1st day of the month to the 21st day of the month for example, the units disc has to make two complete revolutions in order to drive the other disc from 0 to 2.